Because the US population is aging and obesity is rising dramatically, the epidemic of arthritis-associated disability and its associated costs will significantly worsen, largely due to the consequences of knee osteoarthritis (OA). Knee OA is already a major cause of work disability and work absenteeism/presenteeism, and it is responsible for more than 400,000 total knee replacements annually. Weight reduction and increased physical activity can relieve the pain and activity limitations of individuals with knee OA, but these healthy lifestyle behaviors have not been embraced by this large population. The overarching goal of this study is to find an effective, replicable, and sustainable intervention strategy that can assist large groups of employees with or at risk for knee OA to attain and maintain these healthy behaviors. The worksite is an ideal setting to access persons who do not yet have severe knee OA and thus may be more amenable to and benefit more from a behavioral intervention. It is also ideal because both the individual and the environment can be targeted. Our research objective is to further refine, implement, and test the effectiveness of an innovative worksite intervention called JointADventure to reduce the symptoms and activity limitations of knee OA, utilizing a partnership with Blue Cross Blue Shield of Illinois (BCBSIL). BCBSIL is a highly supportive wellness partner, with a strong history of investment in the health of its employees and subscribers. The combined Activity/Dietary (AD) intervention is administered by health professionals trained in motivational interviewing as healthy lifestyle coaches. Over 6 months, they provide 1) individualized counseling based on a comprehensive assessment of baseline clinical, functional and behavioral factors that are barriers to healthy physical activity and dietary behaviors and 2) group education, the content of which is modeled after the highly successful Diabetes Prevention Program physical activity/dietary intervention and customized for those with knee symptoms. Follow-up assessments continue for 6 additional months. Specific aims are to: 1) assess the feasibility of conducting a randomized controlled trial of the JointADventure intervention at this worksite, 2) estimate the effectiveness of the intervention to decrease body weight, improve dietary habits, and increase objectively-measured physical activity, 3) to improve objectively measured functional performance, and 4) to improve self-reported arthritis-specific and generic health status and health utility. If successful, a multi-site randomized controlled trial/R01 proposal will follow to demonstrate the effectiveness/ cost-effectiveness of the JointADventure intervention in larger worksite populations. Given the influence that BCBS has in shaping future health practices and the scalability/generalizability of the proposed intervention, this research could have a tremendous impact on improving symptoms and quality of life for those with early knee OA as well as preventing the work absenteeism/presenteeism, work disability, and increased healthcare costs associated with knee OA.